K60P100M100SF2RM Datasheet, PDF (423/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Peripheral Request
Chapter 20 Direct memory access multiplexer (DMAMUX)
Trigger
DMA Request
Figure 20-20. DMA MUX channel triggering: normal operation
Once the DMA request has been serviced, the peripheral will negate its request,
effectively resetting the gating mechanism until the peripheral re-asserts its request AND
the next trigger event is seen. This means that if a trigger is seen, but the peripheral is not
requesting a transfer, that triggered will be ignored. This situation is illustrated in the
following figure.
Peripheral Request
Trigger
DMA Request
Figure 20-21. DMA MUX channel triggering: ignored trigger
This triggering capability may be used with any peripheral that supports DMA transfers,
and is most useful for two types of situations:
• Periodically polling external devices on a particular bus. As an example, the transmit
side of an SPI is assigned to a DMA channel with a trigger, as described above. Once
setup, the SPI will request DMA transfers (presumably from memory) as long as its
transmit buffer is empty. By using a trigger on this channel, the SPI transfers can be
automatically performed every 5μs (as an example). On the receive side of the SPI,
the SPI and DMA can be configured to transfer receive data into memory, effectively
implementing a method to periodically read data from external devices and transfer
the results into memory without processor intervention.
• Using the GPIO ports to drive or sample waveforms. By configuring the DMA to
transfer data to one or more GPIO ports, it is possible to create complex waveforms
using tabular data stored in on-chip memory. Conversely, using the DMA to
periodically transfer data from one or more GPIO ports, it is possible to sample
complex waveforms and store the results in tabular form in on-chip memory.
A more detailed description of the capability of each trigger (which includes resolution,
range of values, etc.) may be found in the Periodic Interrupt Timer chapter.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
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